Altimeter



Jan. 4, 1949. J, 0, PHELPS ETAL 2,458,022

ALTIMETER Filed Aug. 9, 1944 V 4 Sheets-Sheet l Jan. 4, 1949.

J. O. PHELPS El AL ALTIMETER I 4 Sheets-Sheet 2 FIGB.

Filed Aug. 9, 1944 gwema Jan. 4, 1949. J. o. PHELPS ET AL 2,458,022

ALTIMETER Filed Aug. 9, 1944 v 4 Sheets-Sheet s Jan. 4, 1949- J. o. PHELPS ET AL ALTIMETER 4 Sheets- Sheet 4 Filed Aug. 9, 1944 Patented Jan. 4, 1949 ALTIMETER James 0. Phelps, Richmond Heights, and George W. Cottlill, University City, Mo, assignors to Airpath Instrument Company, St. Louis, M0,, a corporation of Missouri Application August 9, 1944, Serial No. 548,780

' 1s Claims. 1

This invention relates to altimeters, and with regard to certain more specific features, to a settable, flight level indicating altimeter, particularly for aviation use.

Among the several objects of the invention may be noted the provision of a simple, compact and reliable instrument which coordinates flight level indications, a practically readable altitude indication and compass bearing; the provision of an instrument of theclass described having only one simple readable pointer; the provision of an instrument of this class which may beset to indicate flight levels only under assumed standard barometric conditions but which under setting for ncn-standard barometric conditions is readable only as an altimeter, thereby substantially reducing confusion in reading the instru ment under practical flight conditions; and the provision of apparatus of the class describedemploying a very simple mechanical linkage for making desired barometric and temperature corrections. and in part pointed out hereinafter.

invention is an improvement upon the structure shown in U. 3. Patent 2,328,559, dated September 7, 1943.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which is illustrated one of various possible embodiments of the invention,

Fig. l is a plan view of the instrument set for operating under assumed standard barometric conditions with an east compass bearing at 7,000 ft. altitude, and an arbitrary flight level No. 14.;

Fig. 2 is a front elevation of Fig. 1 parts being broken away to show certain details;

Fig. 3 is a vertical section taken substantially on line 3-5l of Fig. 1, parts being broken away behind the section to show certain details;

Fig. 4 is a vertical section taken substantially on line ll-i of Fig. 1;

Fig. 5 is a horizontal section taken substantially along line 5-5 of Fig. 2, various parts being broken away to show features at various adjacent levels;

Other objects will be in part obvious 6 is a horizontal section taken substantially at line il-t of 2, portions being broken away;

Fig. "i is a horizontal section taken substantially on line l-'l of Fig. 2;

Fig. 8 is an enlarged vertical section taken substantially on line 88 of Fig. 1;

Fig. 9 is an enlarged vertical section taken on line 9 9 of Fig. 8; and

Fig. 10 is an enlarged vertical section taken substantially on line Iii-40 of Fig. 1.

Similar reference characters indicate corresponding parts throughout the several views of the drawings.

Present day flight level indicators coordinated with compass bearing means lack means for readan. altimeter and this is impractical.

signed flight level numbers.

ing true altitude whendesirecl. Mental computations must be made if the device is to be used as A difficult problem arises when attempt. is made to. coordinate compassqbearing means with practically readable altitude indicating means. The present invention solves this problem.

Also, the present instrument, when set for assumedstandard barometric conditions, is automatically conditioned for operation as a flight level indicator. When set according to the true prevailing barometric conditions it becomes auto matic'ally conditioned for operation only as a true altimeter readable directly to less than the nearest twenty feet of true altitude above the terrain. Furthermore, the device when operated either as a flight level indicator or as an altimeter is easily read under the respective conditions without confusion. In addition, it is relatively simple in mechanical construction and is arranged for easy, economical assembly.

The invention among other things is designed to meet certain rules regarding arbitrarily as Ihese, for example, are assigned. to the cardinal compass points north. east, south and west respectively. These flight level numbers correspond to predetermined assigned altitudes in feet which prevail for a standard barometer at sea level. Exemplary relationships are shown in the following table, stand-'.. barometric pressure at sea level being assun at 29.92 inches of mercury, but it is to be understood that the invention is useful by suitable adaptation to other arbitrary rules.

Table A Altitude Compass Bearin Feet It will be seen from the above table A, which for convenience is limited to a maximum altitude of 16,000 ft., that 32 arbitrary flight level numbers have been assigned. Flights along north compass bearings are to be made at the even thousands of feet (including zero), plus 500. To these are assigned the flight levels of 1, 5, 9, 13 etc. South compass bearing flights are to be made at the odd thousands of feet altitude plus 500 ft., to which the flight levels 3, 7, 11, 15 etc. are assigned. East compass bearing flights are to be made at the odd thousands of feet altitude, to which flight levels 2, 6, 10, 14 etc. are assigned. The west compass bearing flights are to be made at the even thousands of feet altitude, to which flight levels 4, 8, 12, 16 etc. are assigned.

Thus when a ship bears north, it should always be on an even altitude in thousands of feet plus 500 and will have been assigned one of the flight levels 1, 5, 9, 13 etc. The other assignments that may be made for the other various bearings are clear from the table. These flight levels may be assigned at the airport from which the ship leaves, by radio or otherwise. The pilot is expected to maintain the assigned flight level. This requires him to coordinate compass bearings and flight level numbers. True altitude will, with respect to the terrain, vary according to changes in atmospheric pressure. This is because in the table arbitrary altitudes given are for an arbitrarily chosen standard barometric pressure of 29.92 in hg. at

sea level. Thus every pilot flying under such conditions is at a given relative elevation with respect to all other pilots in the air who are obeying these rules, although all of their absolute altitudes may vary.

The present invention in addition to allowing a pilot to fly conveniently according to the above table A, also provides him with means whereby he may convert his instrument from a mere flight level indicator to one which reads true altitudes 4 under the true barometric conditions prevailing. The flight level indicating features are obliterated under such conditions. This is to avoid confusion. The true altitude readings are then conveniently 5 read to the necessary degree of a curacy. This allows a pilot to descend safely and without confusion through the various flight levels that he needs to negotiate in order to land, and with a complete knowledge of his precise elevational relationship to the field which he is approaching. Referring now more particularly to Figs. 1-4, there is shown at numeral I an airtight case having a conduit connection 3 with a suitable static pressure tube (not shown) for transferring atmospheric pressures to the interior of the case. On its upper edge the case carries an elevated rim 5 and a flange 1. A bezel ring 9 cooperates with the rim 5 and flange T. A gasket I I seals the ring to the case and studs l3 hold it in place. A beveled bezel l 6 is marked with the cardinal com pass points as shown and also in five degree intervals there-between. The flange l and the bezel ring 9 carry extending pocket portions indicated generally at numerals l5 and H for accommodating adjusting mechanisms which will be described later.

Inside of the case I is mounted a frame which has a spider part l9 resting upon a shoulder 2i. i: Extending downward from the spider I9 is a post 23 forming a support for aneroid parts to be described. Extending downward from the spider I9 is also an elongate bearing post 25. Posts 23 and 25 are shown in Fig. 3. Another post 2! is shown in Fig. 4 and serves as an outboard support for 5a drive vmechanism to be described. A fourth post 85 shown in Fig. 3 anchors a spring 83. These posts 23, 25, 2! and 85 constitute all of the main extensions from the spider i9. 221 The post2 3 is split as shown at 29 (Figs. 3 and 0"?) and provided with a screw clamp 3| for holding a supporting stud 33 located on one side of a double-cell, evacuated aneroid element 35. This aneroid element is the prime mover which re- .sponds to barometric pressure changes. A clamp 4511 fastens to the other end of the aneroid element one portion of a bimetallic thermostatic strip 39. This strip has its component of higher coefficient of expansion located away from the aneroid 35. .The length of the strip is enough as shown at (Figs. 3 and 7) for initially adjustably positioning it in the clamp 31 before tightening the latter. The end of the strip 30 is provided with a clevis 4| for pivoting to the strip at center 42 a link 43. At the other end this link 43 is pivoted at center 46 to a lever 45. Lever 45 extends from a transmission shaft 41. This shaft 47 has one fixed bearing 49 in the spider I9. At the other endin a lever 53 it has a movable bearing 5!. Both of the bearings 49 and 5! are preferably of 0 the jeweled variety. It is important for reasons which will appear that they not only permit rotary motion of shaft 4? around its axis but some angular motion of the axis of shaft H. 'The lever 53 is clamped to a rotary pin 55. The clamp 51 is for adjustably positioning the arm 53. The arm '53 also has a clamp 59 for containing the bearing 5|.

The rotary pin 55 is carried on an arm 65 of the post 21. The pin 55 has attached to it a sector gear 6! which has teeth 53 engaging the teeth of pinion 55. The latter is carried upon a rotary shaft 6'! borne in said post 25. This shaft 07 passes through the post 25 to the front of the spider I9 where it carries an adjustable sector gear 69 as shown best in Fig. 6. This sector gear 51; U9 meshes with a pinion M carried on a shaft l3. The latter is borne in boss forming an extension from the spider l9. This boss 15 is pocketed in the extension l5, the latter having a solid enclosing floor. Therefore no leakage of air can occur at this bearing. This is best shown in 10. On the other side the shaft 13 passes through an opening H: in the bezel ring 9. The opening TI is packed around the shaft 73 by means of a rubber grommet 78 which resists infiltration of air. Outside of the rings the shaft 13 is provided with a knurled control knob 19 for setting purposes.

From. the above itis clear that by turning the knob 19 and rotating the shaft 13, movement is transmitted through the gear train H and 69 to the shaft 61, then through the gears 65 and 6| to. provide rotary motion of the pin 55. This rocks the lever 53 and consequently rocks the end bearing 5| of theshaft' 41. It will be remembered that the other bearing 49 of this shaft 4'! is stationary. A slight amount of universal movement permitted in the bearings 49 and 5| allows for the resultin angular movement of the axis of shaft 41 brought about by the swinging of the center 52 of bearing 5|. The direction of swing of the bearing 5| is indicated by the double-ended arrow in Fig. 7. The adjustable angling of the axis of shaft 41 causes an action of the lever 45.

which is in effect a rotary displacement around the center line of the shaft 4'|. This in turn rotates shaft 41 on its axis. The purpose of this will appear.

The shaft 41 is provided with an intermediate arm 8| to the end of whichis fastened one end of the spring 83. The other end of the spring is fastened to the post 85 which extends from said spider l9. Thus the shaft 41 is angularly biased by the spring 83 to cause a pull upon the end of the thermostatic strip 39 and. hence an initial pull is applied to the aneroid (see Fig. 3). This spring takes up the slack in the shaft 4'! and aneroid mechanism, so that there is no play in the bearings 49 and 5|.

From Fig. 7 the essence of the improved control linkage is most clear. In this figure the center of attachment of link 43 to the thermostatic strip 39 is shown at 42. Its center of attachment to the lever 45 is shown at 46. The center of the bearing 5| is shown at 52. The center of the rocking pin 55 is shown at 56. Clearly, if centers 52- and 5B are stationary, as during periods of non-adjustment, then motion of center 42 in response to activity of the aneroid element 35 causes motion of center 45 and angular movement of the lever 45 and hence angular movement of the shaft 41. The final effect of this movement will be traced later. On the other hand, considering centers 42 and 45 relatively fixed (as in the case of a stationary barometer) and an adjustment being carried out from knob 19, such adjustment causes swinging of the center 52 around the center 56, thus pivoting the lever 45 around the center 46. This causes adjusting rotary motion of the shaft around center 52in addition to the axial angular movement of the shaft 41 caused by traverse of the center 52 over the are represented by the double-headed arrow.

At the end of the shaft 41 adjacent to the bearing 49 is attached a sector gear 81 which meshes with a pinion 89 carried on a pin 9| (Figs. 4' and '7) Backlash is taken out of the tooth engagement between the pinion 89 and the sector gear 81 by means of a hair spring 88 attached to the pin 9| .andanchored-to apost 90 extending fionithe spider; t9. Pin tl iiassestnrough a bearing and; the spider [92 This pin on-the able bosses onthe front of the spider ton means of studs 1 M. (one eachof-i thetsupporting bosses and s'tuds isls'hown ior exat'nple stall-03 in Fig. 6; The plate 99 is-by tliis means; held in a plane above: the face of gear plate- 95.- 0n-its edgeit carriesanumerical barometer-scale. A second window I 05 in. the fixed plate 99- is providedforexposing separate flight levelnumbers (see Figs. Land 5-1. The angularrelationshipbetween the successive outer one: thousand. feetwaltitudew numbers and the -innerrow' of'flight'levelnumbers is such that when a given altitude appears' underi window fl, anflight level number will appear under window I 05 whichis double theumagnitude of the other.

The. teeth on thence-gear mesh with acentral pinion INT-carried upon a pin I09; the latter being supported in a bearing 1H at the center of the spider l9; This pin H19 extends through a central opening. H5111 the fixed plate 9.9. The. outeri end orthapimmacarriesa pointer H1 which points to the compass hearings on the bezel 1.5. It alsopointsl td altitude indicating numerals carried on the under face: of? a station-- ary: circular glass window I I5. This. gl'assisprovidedwi'tha notch 2 (-Figsi 3 arrdfi) which engages with-a pin 4, the-latter. being anchored in the. rim 5.

The pointer H1 is located in a plane above a barometer index'ring M4,; the. latter having a radial flange I23 to provide albearing surface on. atop rim. |25 of. thespider l9". Inside of the rim I25 teeth i2! are provided. on" the hacklofring |2|. These mesh with another gear I28 whichis carried ons'aid. shafti 133:. Thus by turnin the knob 19 a second-gear train is brought into operation, namely,.gears I28 and M1, thus turning the barometer index ring. I21; an inner. rim 129. which isannular. in form as indicated in Fig 1. It is notched out-as shown" at. |3| andthebase: of the notch is provided with a pointer |33 whichxplays" over. the barometric scalemarked off on the: rimoi plate H9.v The scale is marked ofii' in inches of mercury. Tenths and hundredths of. inches of mercury are marked under the rim I29 and are exposedlonlyrby' reg, istry of notch |3|.. avoids confusing additional fractional. scale markers which would otherwise appear. Whole-inchindices are preferably always exposed since: they are not confusing. If desired they alsowmay'b'e placedunder the rim I29and exposed only by-the notch "I.

The barometric pointer ring: carries: on its under side a camming lug. I35 (see F15.- 8 and 9) which during addusturentot the-ring. is engage;-

able with a finger I31 of'a; semaphore shield l39,

the latter being pivoted at I to the bottom of the window plate .99. This shield. I39 swings across the bottom of the fiightlevelwindow H15. Inverticalposition (solid linesrFlg. 9-) it covers the window and in the alternativewdottedeline positions uncovers it. 1 Amery small angular-move?- mentof thead justmgrrina .izt-serves touncover Theouter ring of characters represents the window I 015. The lug I35 is so positioned with respect to the, pointer I33. on ring I2I that the shield I39is. in either ofits dotted-line open positionsonly when the pointer I33 is at or very near the standard barometer setting, namely when indicating 29.92 in. hg., as shown in Figs. 1 and 9. In other words, a flight level reading may be taken only when the instrument is set for the assumed standard barometer.

Inorder normally to hold the. shield I39 in its covering position underneath the window I05 (when disengaged by the lug I35), a piano-wire spring i43jis attached to itsbase I41 as at I45 (Fig. 9). This. spring reaches to and through a hole in a rotary pivot I 49 extending from beneath the plate 99. Thus when the finger I31 of the shield I39'is released by the lug I35, the shield I39 will spring from either of its dotted-line positions shownin Fig. 9 to the solid-line position. Only one of the dotted-line positions of the shield I39-is showninFig. 1. Itwill be understood that two: of themoccur, depending .upon what direction the finger.=I31 is approached by the lug I35. Referring to Fig. 1, if it is approached from the top, then the shield I39 assumes the dotted-line position shown. If it were approached from the bottom, the shield would assume the other dottedline position not shown in Fig. 1 but shown in Fig. 9. 1

As above mentioned, thestationary glass H9 carries index numerals to which the pointer II1 relates. These numerals indicate hundreds of feet of elevationrplus .suitable subdivisions of twenty feet each which may be further subdivided by ;,interpolation. The dial has two marked segments, each starting with zero on opposite horizontal sides of the instrument and extending to 1,000 by 100 it. marked increments, making a 1,000 ft. total for each 180 of index on the glass (Fig. 1). The reason for this double scale will appear.

The glass Il'9is supported on a packing ring I5I which in'turnis supported upon a seating ring I59. The ring I53 is supported upon the rim 5. It spans a gap I55 in the rim 5 which gapisneeded for passage of the gear trains 69,

11 and H8, H1, above mentioned. The bezel I6- of the bezel ring 9 extends over the edge of a circular plastic window sheet I51. This sheet on its edge rests upon but is rotary with respect to a packing ring I6I. This ring, beyond the edge of the window I51 is gripped between the bezel I6 and the glass II9, thus sealing again-st air leakage. As indicated. in Fig. 5, the ring I5I is slightly convoluted so that when the bezel ring 9 is drawndown by the studs I3, all of the non-rotary partsllil,v I5I and I53 will betensioned against vibration.

From Fig. 10it will be noted that the edge of the plastic window I51 is provided with teeth I59. "These teeth are meshed witha pinion I63 locatedn-on a pin 55 which passes through the bezel 'ring9and is located in the region of said extension- I 1' (Figs. =1 and An outside knurled knob M31 provides means for -turning the pinion Hi3 and hence the plastic window I51. On the inner surface of this window are spaced guide arrows I09 between which the pointer II1 may be aligned. J

-Mchanical operation in response to changes i atmospheric pressure is as follows:

Expansion or "contraction of the aneroid 'element '95 results in' linear movement of the clevis M which transmits motion through the link 43 to thelev'er 45; thus rotating the shaft 41 in the bearings 49 and 5I. Spring 83 takes up the slack. This rotary motion is transmitted to the sector gear 81 which drives pinion 89. This rotates the counter gear plate 95, thus presenting behind window 91 a figure representing thousands of feet of elevation. At the same time it presents the proper figure behind the Window I05 (when opened) representing the corresponding flight level by a number twice the value of the number behind the window 91. At the same time the gear 95 through pinion I01 drives the hand or pointer II1 to indicate the additional it. values of elevation, along with their interpolations. The gear ratio between gears 95 and pinion I01 is such that for each 1,000 ft. of change indicated through the window 91, the pointer I I1 rotates figures on the glass II9 will indicate values beyond any even number of thousands of feet rep-.

resented through window 91; whereas'the lower segment of figures on the glass II9 will register values beyond odd thousands of feet represented through window 91.

The bimetallic strip 39 compensates for temperature changes in the aneroid element. For example, a higher temperature which expands any residuum of gas in aneroid 35 tending to push clevis 4I out too far is olTset by bending of the bimetallic strip 39 toward the aneroid.

Operation to adjust for barometric changes is accomplished as follows:

The knob 19 is turned so that the pinion 1| (Fig. 6) drives the sector gear 69. This drives shaft 61 and pinion 65. This in turn drives the sector gear SI which rotates the pin 55 and the lever 53. This swings the lower bearing 5| of shaft 41, thus rocking the shaft angularly from end to end, causing the endwise motion indicated by the double arrows in Fig. 7.

This has the effect not only of angularly swinging the axis of the shaft but of providing it with a component of rotation around this axis. The reason for this has above been made clear. The result is that the sector gear 81 is rotated. This drives the pinion 89 and causes the counter gear 95 to move and indicate both a corrected e1evation and flight level. In other words, true elevation from sea levelis obtained by correcting an amount corresponding to the equivalent elevational error brought about by barometric changes. The required amount of adjustment is indicated through the operation of the gear I29 on the teeth I21 of barometric indicating ring I2I'. This causes the pointer I33 to indicate the barometer value to which the setting has been made. As is known, altitude corrections for barometric changes are not in a straight line proportion. That is to say, one inch of mercury at sea level represents a smaller difference in elevation than one inch at altitudes above sea level. The linkage proportions and arrangements shown in the drawings establish proper relationshipssubstantially to account. for this inequality. Thus-thepointer [3.3 indicates. at the rim of the window plate 99 the barometric pressure prevailing according to a given adjustment. The scaleo'n the rim of the plate 99 is even, while the amount of correction indicated by corrective movementof face gear plate 95, because of the character of the corrective linkage, varies with altitude. Furthermore, when the pointer I33 is at standard barometer (29.92 in. hg.) as indicated in Fig. 1, the lug I35 has caused the shield I39 to move away from'the flight level window I05. At all The upper segment of' @MEOEQ to cover the window .byispringwlfl.

The adjustable transmission mechanism is quite simple. important feature to note in connection withit is that the end-of the'shaft '4'! near the :aneroid 135 "is substantially swingable for adjustment purposes but the end near the fixed bearing 59 moves very little. .It is at this end of small movement that the .gear train 81., .39 is positioned. Therefore themeshing action between the gears 81 and 89 is not interfered with toany extent .thatis appreciable. Slight backlash introduced is takenupby the action of spring 88.

Complete functionaloperation, from the-view- 1 point of a pilot operating a. plane with the device,

is as follows:

Upon starting a trip the pilot determines his compass course from a suitable chart, and for example assuming thatiit is due east, herevolves assigned, which for an east course, according to,

table A, may be any of. levels 2, 6, :10, 14, 18,22, 26 or 30 for the instrument shown. As indicated in Fig. -l the particularflig ht level 14 has been .assigned, which accords to an altitude of 7,000 ft. above sea level, based upon a standard barometer, but under cruising conditions the .fact that this altitude may be somewhat in error due to nonstandard barometric c'onditions isrinconsequential since all other pilots in the. air are operating with the same error which properly relates them one to the other. The assignor of the flight level number of course makes sure thatythe general altitude is high enoughito clear the terrain to be traveled. But the important thing .to the pilot now is that he will be correctly related to other ships on other flight levelsoperatin g according to the rules. To fly properly, the. pilot simply brings the proper flight level number 14? before thewinclow I05 'andthe pointer Ill into the due east position shown, without manipulation of the instrument as such. This, is done by elevating the ship. In other words, he brings the ship to an elevation whereby flight level number 14 is brought into view at thewindow I Elli and whereby the pointer Ill moves into the previously set directing band H59, that is,,pointing due east on the bezel 16 This may require several revolutions of the pointer Ill. .If a particular flight level is not assignedit is only important .in order to obey, the rules that thepilot be on one. of the correct flight levels for his east compass course, that is to say, on any one of flightlevels 2, 6, 10, 14, 1 8, 22, 26 or 30. Thus a pilot needs merely to glance at the instrument in adjusting the elevation of his ship and hold the latter such that ing to maintain a desired track. This will require .a slight change in elevation to accord with the required bearing andhas the advantage that ships of difierent-speeds operating over the same direotional'track will be at slightly difierent elevations because of the different bearings required by ships of different speeds operating in the same cross-wind. This advantage "is not true whenthere is not a cross-wind but it is to be the pointer l l! is simply between the pre-setlines at flight level 14. WItis to .beunderstoodthat drift may require the pilot to. .fiya corrected beatobserved that under the latter conditions the trailing pilot has'the leading pilot directly in his line'ofsight and under such conditions a collision between two shipseven at the same altitude is rarely to 'beexpected. Underall otherconditions the ships will be automatically separated.

Each time that a 1;000 unit diiference occurs in the window 91, the pointer It! moves through 180,thus indicating I interpolations of less than 1,000 ft. It will now "beclear that the upper segment of numbers on glass H9 reads the even thousands in window 9! plus 1,000 ft.; whereas 'the'lower segment'reads odd thousands of "feet in the window-9lplus'lg000 by interpolation. Stated otherwise, either 1'80 segment coordinates with the pointer I llto .interpolate elevation but one group (the upper one) is 'associatedwith the even thousands of feet elevation in the thousands window *QIandthe other group (the lower one) is associated with "the odd thousands of feet elevation in the window 91. allows of one pointer I I! being effective to indicate the relative elevationand'the compass bearing atom and the same time.

Should azpilot during flight need to change his bearing :he fsimply does :so by turning the knob 161 to adjust th'eindex bandilfill for the desired new compass course,;and then adjusts his shipto bringthe needle intovthe band. For example, he may want to switch to a south course in which event ,guide I69 ispl'a'ced vertically, pointing down. The-shipis then brought up to a point? where pointer 'Hlwill be vertical andpoint downward. This --will automatically :place the ship on'one of flightlevels 3, 7,11, 15, .19, '23, 2V or 31. The pilot may *choose any of-these and be safe, in'-. cluding any particular one that may be assigned by radio "or otherwise. Intermediate compass bearings arehandled similarly, the closest as signed flight levelnumber appearing at window I 05 and the actual flight level being iractionally correct due to the .proper setting of the pointer IT. For example, if intermediate headings between the .cardinal compass points are; desired, these may be followed by settingthe pointer L69. If in Fig. 1 the pointer H l were to point south by east a ship level would be assumed twothirds of the way b'etweenflevels 14 and 15, flight level 15 being associated with a southcourse. The various flight levels of different airplanes will be sp'acedproperly even though the barometric pressure changes, provided the pilot, as he should, allows the barometer pointer I33 to remain at standardbarom'et'er setting.

Assum'enext that the pilot wishes to land. For this-purpose it is necessary thathe knowh'is absolute elevation with respect to the actual elevation of the airport. The latter he obtains by radio or knows from his chart. In *order to obtain his own actual elevation as distinguished from elevation relative to other ships, the device to be used as an altimeter :must be corrected for the prevailing barometeroonditions. Assuming that he :receives barometer i-information by radio, he sets the pointer 1:133 toindi'cate it. This isdone tromknobwla. This immediately mo'vesfithe lug 935 from. cooperation with the shield l39'and the latter springs over the flight level window I05. Any confusion from this source is therefore eliminoted. The instrument thus instantly becomes converted into a simple true altimeter. The pilot now has before him an altimeter reading corrected for barometer and he simply reads the elevation from the thousand foot elevation data behind the window 91 and the interpolation on the periphery of the glass H9 as determined by the pointer H1. When his elevation is equal to that of the port which he is approaching he is in landing position. All confusion is avoided. The instrument may be referred to as a convertible altimeter and flight level indicator.

In the present embodiment the means for effecting traverse of the 1,000 ft. gross altitude indicating numbers behind window .91 may be referred to as a gross-unit altitude indicator. It will be understood that an equivalent of. this would be the use of another pointer associated with the pointer I I1 and traversing a dial indexed in 1,000 ft. intervals. Although this would be less simple to read, many of the advantages of the invention would be retained even with its employment. In other words, the construction could be used not unlike a clock wherein gross altitude indications would be shown by a pointer not unlike an hour hand and interpolated indications would be shown by the pointer H1 not unlike a minute hand.

It will also be clear that the multiple interpolated-unit ranges with which the pointer ll! cooperates may be made up in other multiples than the two shown, in order to provide a desired coordination between compass bearing and altitude reading in cases where other measuring units or rules are adopted than those shown in table A. For example, if hereafter flight level numbers might be coordinated with altitudes in other than gross 1,000 ft. intervals it might be necessary to spread a given interpolating scale over other than a 180 arc. Furthermore, in the metric system gross-unit increments behind window 91 may be different; also the interpolated-unit increments on glass H9.

Not only does the instrument have the operat ing advantages stated but it is structurally quite simple, particularly as regards the mechanical arrangement for barometer corrections whereby the one bearing 5| of the transmission linkage is simply swung.

Another feature of the mechanical simplicity is that the bearings for the various fixed and rotary parts above the spider l9 are arranged, so that it is a simple matter to apply one afteranother from the top of the instrumentas assembly proceeds.

It will be understood that the device may be adapted to the gyro autopilot as a means of automatically controlling the altitude being flown. This would be done by interconnecting the control knob I61 (which controls the course pointer I69) with the autopilot so that when the pointer 169 is set to the proper course, and hence to the proper altitude or flight level, the autopilot will send and hold the ship to a proper selected level.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all'matter contained in the above description or showni'in" the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

We claim:

1. An altimeter comprising atmospheric pressure responsive means, a 1,000 ft. gross increment altitude indicator driven by said pressure responsive means, an altitude dial showing interpolated altitude increments of less than 1,000 ft., said dial being separated into two segments each of which indicates a gross total of 1,000 ft. by increments less than a thousand feet, a pointer driven from said pressure responsive means and traversing 360 of the dial for each 2,000 ft. indicated change in said gross thousand foot indicating means, and a compass dial adjacentto the altitude dial and also traversed by said pointer, two cardinal points of the compass dial being fixed adjacent to the ends of said two segments.

2. An altimeter comprising an atmospheric pressure responsive means, a fixed compass dial, a gross-unit altitude indicator and a pointer traversing the copass dial and both being driven by the pressure responsive means, an altitude dial laid ofi adjacent to the compass dial with units interpolating said gross units, said altitude dial being traversed by the pointer and being indexed with multiple numerical ranges each starting at zero at a cardinal compass point.

3. An altimeter comprising atmospheric pressure responsive means, a 1,000 ft. indicator driven by said pressure responsive means, a dial divided into two segments each of which has index means indicating a total of 1,000 ft. by increments of value of less than one thousand, a pointer driven from said pressure responsive means and having movement related to the 1,000 ft. indicating means so that it traverses 360 of the dial for each 2,000 ft. change in said thousand foot indicating means, and a fixed compass dial related to the pointer so that at certain even values of the 1,000 ft. indicating means one compass bearin is indicated, and whereby at certain other even values the opposite compass bearing is indicated.

4. Analtimeter comprising atmospheric pressure responsive means, a 1,000 ft. indicator driven by said pressure responsive means, a dial divided indicating a total of 1,000 ft. by increments of value less than one thousand, a pointer driven from said pressure responsive means and having movement related to the 1,000 ft. indicating means so that it traverses 360 of the dial for each 2,000 ft. change in said thousand foot indicating means, and a fixed compass dial organized with the pointer whereby at uneven values of the thousand foot indicating means one compass bearing is indicated, at even values the opposite compass bearing is indicated, and whereby at uneven values plus 500 another compass bearing is indicated at to those first mentioned, and at certain even values plus 500 a compass bearing is indicated opposite to the bearing last mentioned.

5. An altimeter comprising an atmospheric pressure responsive means, a compass dial, a gross-unit altitude indicator and a flight level indicator driven by said pressure responsive means, a pointer traversing the compass dial and inaccordance with barometric pressure changes to bring about true indication of elevation, a shield adapted to cover and uncover said flight level indicator, and cooperating means between the adjustable means and the shield whereby the latter shields from sight the flight level indicator except at a predetermined setting of the adjustable means.

6. An altimeter comprising atmospheric pressure responsive means, a gross-valued altitude indicator driven by said pressure responsive means, a dial ShQWll'lg altitude increments less than the gross values, said dial being separated into-two segments each of which indicates by increments a total summing up to said gross value, a pointer driven from said pressure responsive means and having movement related to the gross-valued indicating means so that it traverses 360 of the dial for. two of the gross values, and a fixed compass dial organized with the pointer.

'7. An altimeter comprising atmospheric pressure responsive means, a 1,000 ft. indicator driven by said pressure responsive means, a dial indexed with altitude increments of less than 1,000 ft, said dial being separated into two segments each of which indicates a total of 1,000 ft. by increments less than a thousand, a pointer driven from said pressureresponsive means and having movement related to the thousand foot indicating means so that it traverses 360 of the dial for each 2,060 ft. change in said thousand foot indicating means, and a fixed compass dial organized with the pointer whereby at certain indicated elevations certain compass bearings are also indicated.

8. An altimeter comprising an atmospheric pressure responsive means, a fixed compass dial, an altitude dial havin numbers representing relatively small values and traversing the entire compass dial and starting at zero at two opposite points on the diaLan indicator having numbers representing relatively large values, a pointer for the altitude and compass dials, and a mechanlsm connecting said pressure responsive means, the pointer and the indicator whereby each relatively large value represented on the indicator is associated with a sequence of the relatively small values represented on the dial, said pointer pointing simultaneously to compass bearings on the compass dial.

9. An altimeter comprising an atmospheric pressure responsive element, a fixed compass dial, a pointer for said dial, a gross altitude indicator carrying a sequence of numbers, an altitude indicating dial arranged adjacent to the compass dial and traversed by said pointer, the altitude dial having tier-eon repeating sequences of numbers representing fractional parts of the values indicated between successive numbers on the gross indicating dial, and means connecting the pressure responsive means, the gross altitude indicator and said pointer whereby the pointer travels one of said sequences of numbers on the altitude dial for each change in indication represented by adjacent numbers on said gross indicator.

10. An altimeter comprising an atmospheric pressure responsive element, a compass dial, a pointer for said dial, a gross altitude indicator carrying a sequence of numbers, an altitude indicating dial arranged adjacent to the compass dial and traversed by said pointer, the altitude dial having thereon repeating sequences of numbers representing fractional parts of the values indicated between successive numbers on the gross indicating dial, means connecting the pressure responsive means, the gross altitude indicator and said pointer whereby the pointer travels one of said sequences of numberson the altitude dial for each change in indication represented by adjacent numbers on saidgross indicator, and a fiightlevel indicator indicating in a proportion to the change indicated by thegross indicator. i i r 11. An altimeter comprising an atmospheric pressure responsive element, a compass dial, a pointer for saiddial, a gross altitude indicator carrying a sequence of numbers, an altitude indicating dial arranged adjacent to the compass dial and traversed by said pointerythe altitude dial having thereon repeating sequences'of numbers representing fractional parts of the values indicatedbetween successive numbers on the gross indicating dial, means connecting the pressure responsive means, the gross altitude indicator and said pointer whereby the pointer travels one of said sequences of numbers on the altitude dial for each change inindication representedby adjacent numbers on said gross indicator, a flight level indicator indicating in a proportion to the change indicated by the gross indicator, a movable shield for theflight level indicator, adjustable means for correcting altitude and the flight level indications to true barometric conditions, and means coupling the correcting means and the shield to removethe shield fronrthe flight level indicating means at a predetermined standard settingof the adjustable means.

12. An altimeter comprising an atmospheric pressure responsive means, a compass dial including cardinal compass points, a thousand foot indicator and a pointer for the compass dial, a hundred foot altitude dial laid off adjacent to the compass dial and having two ranges each totaling 1,900 it, each starting at zero at opposite cardinal compasspoints, aflight level indicator indicating in a proportion to the thousand foot indicator, operative means interconnecting the pressure responsive means with the thousand foot indicator, the flight level indicator and the pointer, settable barometric adjusting means for changing altitude and flight level indications according to the barometer, and means coordinated with said adjusting means .ior hiding from view the flight level indicator under all barometric pressures except standard.

13. An altimeter comprising an atmospheric pressure responsive means, a compass dial including cardinal compass points, a gross-unit altitude indicator and a pointer for the compass dial, an altitude dial laid ofi adjacent to the compass dial and having .two ranges each totaling one of said gross units, each starting at zero at opposite cardinal compass points, a flight level indicator indicating in a proportion to the gross unit indicator, operative means interconnecting the pressure responsive means with the gross unit, altitude indicator, flight level indicator and pointer, settable barometric adjusting means for changing altitude and flight level indications according to the barometer, and means coordinated with said adjusting means for hiding from view the flight in a proportion to the 1,000 ft. indicator, operative means interconnecting the pressure responsive means with the thousand foot indicator, the flight level indicator and the pointer, settable barometric reference means for changing altitude and flight level indications according to the barometer, means coordinated with said adjustable reference means for hiding from view the flight level indicator under all barometric pressures except standard, and a barometric scale to which said reference means is referred.

15. An altimeter comprising a movable atmospheric pressure responsive element, rotary pressure indicating means, mechanism connecting said pressure responsive means with said rotary indicating means comprising a rotary transmission shaft, driving means between said shaft and said rotary indicating means, a link connection between said shaft and said pressure responsive means, a fixed bearing for the shaft, a second bearing therefor normally stationary, adjustable means for bodily moving the second bearing perpendicular to the shaft axis to angularly move the transmission shaft axis, adjusting movement ofsaid second bearing causing a relative rotary motion of the transmission shaft with respect to said linkage whereby adjusted rotary motion may be applied to the indicator in addition to a rotary motion obtained through action of said pressure responsive means.

16. An altimeter comprising a substantially flat supporting spider, indicating means on the spider, an aneroid supported on said spider with its general plane normal to the general plane of the spider and expansively movable parallel to the spider, a rotary shaft having its axis normal to the spider and substantially parallel to the aneroid, said shaft having a fixed pivot near the spider, gear means adjacent the fixed pivot for driving said indicating means on the spider, a movable pivot supporting the other end of the shaft adjacent the aneroid, rotary means supporting said movable pivot, an adjusting gear train for actuating said rotary means, a lever extending from said shaft adjacent the aneroid and between said movable pivot and the fixed pivot, and a connecting link pivoted to said lever and pivoted to a part on the aneroid whereby linear motion of the aneroid may be translated into rotary motion of the shaft, adjusted rotary motion of said support for the movable pivot causing rocking of the shaft about the fixed pivot, whereby the shaft is also adjustably rotated.

17. In apparatus of the class described, an altitude indicator including means for indicating altitude in terms of distance and in termsof flight level indicia, means responsive to barometric pressure for operating said altitude indicator, means for adjusting said altitude indicator in accordance with prevailing barometric pressure or in accordance with a predetermined standard pressure, whereby said altitude indicator indicates either substantially the actual value of the altitude or an arbitrary value, and means including an adjustable shield actuated by said adjusting means for concealing the flight level indica of said altitude indicator when said indicator is adjusted in accordance with all barometric pressures except said predetermined standard pressure.

18. An altimeter comprising an atmospheric pressure responsive means, a fixed compass dial, an altitude dial having numbers representing relatively smallvalues and traversing the entire compass dial and starting at zero at two opposite points on the dial, an indicator having numbers representing relatively large values, a pointer for the altitude and compass dials, a mechanism connecting said pressure responsive means, the pointer and the indicator whereby each relatively large value represented on the indicator is associated with a sequence of the relatively small values represented on the dial, said pointer pointing simultaneously to compass bearings on the compass dial, and adjustable means for changing the readings of the pointer and theindicator in accordance with barometric pressure changes to bring about true indication of elevation.

19. An altimeter comprising an atmospheric pressure responsive element, indicating means, a rotary transmission shaft for transmitting movement from the pressure responsive element to the indicating means, said shaft bein journalled at one end in a stationary bearing and at its other end in a laterally movable bearing, an extension from said shaft adjacent said movable bearing, a link connecting the pressure responsive ele ment and said extension to rotate the shaft about its axis upon changes in atmospheric pressure. and adjustable means for laterally moving said movable bearing, whereby adjusting rotation may be applied to said shaft;

JAMES O. PHELPS. GEORGE W. COTTRILL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,208,728 Menzer July 23, 1940 2,258,826 Torkelson Oct. 14, 1941 2,328,559 Knight Sept. 7, 1943 

